Currently double walled combustors have an inner wall comprising a plurality of tiles. The tiles have studs that are integral with the tile for attachment to an outer wall. Conventional tiles have pedestals on their outer surfaces to provide cooling of the tiles.
Advances in gas turbine engine technology have resulted in an increase in temperature with increasing focus on emissions regulations, and consequently the pedestal cooling arrangement of the tiles may be superseded by an impingement effusion cooling arrangement of the tiles.
Tiles with an impingement effusion cooling arrangement have an array of effusion cooling holes arranged at a relatively low angle, typically twenty degrees, to the tile surface. Forming these holes at the angle required leads to manufacturing difficulties, due to the clash between a laser head and the protruding studs. As a consequence, the resulting tile either has a significant area around each stud that is devoid of effusion cooling holes, or alternative approach vectors have to be defined so that the laser head avoids clashing with the studs. The alternative approach requires extra programming time, extra manufacturing time, and leads to a compromise in the X and Y positioning of the effusion cooling holes on the tile surface, and the ‘a, b, c angular definition of the hole vector’.
In some arrangements of non-pedestal tiles the studs which are an integral part of the tile, and which protrudes through the combustor outer wall, are replaced with alternative arrangements which are disclosed in U.S. Pat. No. 5,079,915 and U.S. Pat. No. 4,085,580. In both of these arrangements the tile is provided with a threaded receptacle into which a bolt is inserted through the outer wall. The end of the receptacle abuts the internal surface of the outer wall and helps define the depth of the air flow channel which has an optimum depth to maintain a desired flow speed. Additionally, where pedestals are provided, the receptacles ensuring the pedestals abut the inner surface of the outer wall to aid heat transfer away from the combustor tile.
The securing arrangements described in U.S. Pat. No. 5,079,915 and U.S. Pat. No. 4,085,580 require a minimum number of thread turns to securely mount the tile on the outer wall. This may lead to the depth of the air flow channel being too great for the pedestals to make contact or the flow area being too great, thereby reducing efficiency, as more air is required for cooling, and as a consequence less air is available for diluting the combustion.
It is an object of the present invention to provide an improved combustion chamber.